It is well known that various liquid petroleum hydrocarbons, such as petroleum-derived fuels (e.g., gasoline, jet fuel, diesel fuel, heating oil, kerosene, lubricating oil) can be marked or tagged for identification purposes with visible dyes at dosage levels that impart a distinct color to the fuels perceptible to the human eye. Historically, yellow, red, blue, green, and purple solvent dyes, along with other solvent dyes that strongly absorb radiation in the visible portion of the electromagnetic spectrum, have been used as such fuel colorants.
The need to tag fuels to provide means to distinguish them from seemingly identical products exists for a number of reasons, including to identify various grades of fuels, to distinguish manufacturer's brands, to differentiate similar fuels taxed at different rates, and to make adulteration, counterfeiting, misuse, tax evasion, and theft impossible or at least traceable. The need primarily arises from differing price or tax structures of different fuels or even the same fuel used for different purposes and the opportunity in these situations for unscrupulous persons to cheat or abuse the tax laws.
For example, it is common for governments to require coloring of lower taxed fuels to provide means to distinguish them from similar fuels subject to higher taxes and detect tax evasion. Unscrupulous persons can make large profits simply by purchasing lower taxed fuels and selling them at the higher taxed fuel prices, or by diluting higher taxed fuels with lower taxed fuels and selling the diluted product again at the higher taxed fuel prices. C.I. Solvent Red 26 is currently used by the U.S. Internal Revenue Service to distinguish non-taxed home heating oil from other taxed fuels of identical composition yet used for different purposes, such as diesel motor fuel. If red dye is present, no federal taxes have been paid on the product. Presence of red color in the product is taken as evidence of tax evasion if the fuel is sold as taxed commercial diesel fuel.
Aside from tax matters, fuels are colored by major oil companies that market brand name products such as gasoline to prevent misuse by their dealers. Oil companies go to great expense to ensure their branded products meet stringent specifications regarding volatility and octane number, as well as to provide them with effective additive packages containing detergents and the like. Consumers rely upon the company's trademarks to assure themselves that the product being purchased is of high quality. Unscrupulous gasoline dealers can make large profits simply by diluting or substituting the brand name product with an inferior product and selling the resulting inferior product at the price consumers are willing to pay for the branded product. For example, it is possible for dealers to cheat by blending lower priced products such as kerosene, heating oil, or diesel fuel into regular grade gasoline or blending regular grade gasoline into higher priced premium gasoline and selling the inferior product at a premium price. Colored fuels thus provide oil companies with means to visually distinguish brand and grade denominations and police their dealers.
Another valuable function of fuel colorants is for identification of particular production batches of bulk liquids for protection against theft, particularly for identifying fuels owned by large government, military or commercial consumers. Fuels are also dyed so that oil companies can identify their branded products from others', particularly when faced with product warranty, product liability, and pollution claims.
Yet, it is also known that visible dyes, when used as fuel colorants, are not always reliable for tagging purposes. While it may be extremely difficult, it is not impossible for unauthorized persons to selectively remove visible dyes from the fuels. For instance, one form of deception in the past has been to decolorize non-taxed heating oil with absorbents, such as activated charcoal, and then sell the colorless product as higher priced diesel fuel. Another problem is that the color imparted by visible dyes may be obscured by natural substances or additives present in the fuels, making visual color recognition extremely difficult. High dosage levels (e.g., 25 to 100 ppm) are also needed for visual detection, which creates other problems, such as increased costs.
Because colorants alone have such shortcomings, there has been a growing desire to mark or tag fuels with, in addition to or in place of the dye colorant, markers or taggants that impart no visual coloration to the tagged product, yet are still detectable by a quick and simple chemical or physical test procedure. Markers that are not visually discernable to the unaided eye in the tagged product at the levels which they are used are termed "silent" markers or taggants. Silent markers, accordingly, identify a product only to an authorized tester and do not provide any visual indication of the identity of the product to the regular observer or those parties interested in violating brand or product integrity. Adulteration and misuse of fuels, therefore, becomes much more difficult. For instance, even if unscrupulous persons attempt to remove such markers to the point of non-detectability, they will never be able to determine whether their laundering efforts were successful without knowledge of the marker utilized or access to the authorized tester's detection equipment. Traditionally, there have only been relatively few silent markers available.
There are also a number of drawbacks associated with the currently available silent markers. Many require chemical manipulation of a fuel sample for detection which generates waste materials necessitating disposal. These markers are typically fuel soluble visible dye precursors which are virtually colorless compounds when employed at recommended dosage levels, yet are known to react with selected reagents to from intensely colored derivatives, as for example, as taught in U.S. Pat. No. 4,209,302 (Orelup). Chemical detection normally requires extraction of the marker with an acidic or basic aqueous liquid extractant, followed by addition of a reagent to cause the extract to turn a visibly distinct color, although in some cases, the reagent is unnecessary. While effective, this procedure has a couple of drawbacks. For instance, it is time-consuming to perform. It also does not provide a good quantitative measurement of marker concentration in the field. Quantitative determinations are particularly important in cases where dilution is suspected. For a rough estimate of marker level, inspectors in the field are given color charts against which to compare the developed color intensity to determine fuel identity and extent of dilution. However, laboratory verification is needed to confirm the marker concentration. Lastly, the tested by-products must be handled and disposed of as hazardous waste, which is manifestly cumbersome.
Truly silent markers which are not visible at any concentration have also been proposed for invisibly tagging petroleum products. These markers are typically large organic molecules that have virtually no absorbance in the visible portion of the spectrum and that absorb and/or fluoresce in the near infrared to mark their presence in a fuel sample. U.S. Pat. No. 5,525,516 (Krutak et al.) and European Patent 0,656,929 (Albert et al.) describe such markers. In these references, the presence of such a marker is detected in the fuel by exposing the fuel to near infrared radiation and then either detecting the characteristic light absorption spectra of the marker or its emitted fluorescent light in the near infrared region with standard absorption or fluorescent detection equipment. While the detection procedure is much simpler, molecules or markers that are active in near infrared are large, complex, organic structures. Therefore, these markers are difficult and expensive to make. Furthermore, there are only a finite number of near infrared absorbing or fluorescing molecules that can serve as silent markers, since many of these molecules absorb in the visible portion of the spectrum as well.
In sum, few practical markers exist and even fewer practical silent markers exist. Furthermore, many silent markers are expensive or not user friendly in that a user must chemically manipulate a fuel sample and handle and dispose of potentially hazardous chemicals. With the growing drive to prevent brand adulteration of fuels and to authenticate fuels, and the widening use of markers around the world for fiscal marking and enforcement of taxation, more silent markers and improved methods for invisibly marking and identifying petroleum products are needed.
Never before had one skilled in the art thought it possible to use visible dyes as silent markers, rather than as colorants, for liquid petroleum products until the present invention. This use of visible dyes by its very nature is highly unexpected.